In order to improve properties of various base materials, a film has heretofore been formed by vapor deposition on their surfaces by the plasma CVD method. In the field of packing materials, for instance, it is a known practice to form a film by vapor deposition on a plastic base material such as of a container relying on the plasma CVD method in order to improve the gas barrier property.
For example, there has been known a method of producing a plastic container by forming a vapor deposited film (barrier layer) containing a silicon oxide and a compound of at least one kind of element selected from carbon, hydrogen, silicon and oxygen on the outer surface or the inner surface of the plastic container relying on the plasma CVD method by using an organic silicon compound and oxygen or a gas having an oxidizing capability, while varying the concentration of the organic silicon compound (see patent document 1).
A gas-barrier film has also been known comprising a base member, a gas-barrier layer (vapor deposited film) formed on one surface or on both surfaces of the base member, and a water-repelling film (water-repelling layer) formed on the gas-barrier layer (see patent document 2).
Patent document 1: JP-A-2000-255579
Patent document 2: JP-A-2003-53873
The vapor deposited film formed by the method of the patent document 1 may exhibit excellent barrier effect against various gases such as oxygen and the like but has low durability against water permitting silicon to elute out in an alkaline aqueous solution such as mineral water. In the field of packing materials, therefore, it has been desired to improve the adhesion of film to the base material and such kind of elution. A gas-barrier film disclosed in the patent document 2 exhibits durability which is improved to some extent against water since a water-repelling layer has been formed on the surface of the gas-barrier layer which is the vapor deposited film. However, the degree of improvement is not sufficient. Even by forming the water-repelling layer, therefore, it is not possible to sufficiently suppress the elution of silicon into the alkaline aqueous solution.
The vapor deposited film of a metal oxide as represented by a silicon oxide exhibits a high gas-barrier property but lacks flexibility and exhibits a low adhesiveness to the base material on which the film is vapor deposited and, particularly, to a plastic base material. Therefore, in case the film is vapor deposited on a plastic container or the like, the vapor deposited film cannot follow the deformation of the container caused by the expansion or the like, arousing a problem of a great decrease in the gas-barrier property.
To avoid the above problems, the present applicant has previously proposed forming a vapor deposited film by adjusting the reaction conditions at the time of forming a vapor deposited film of a metal oxide by the plasma CVD method by, first, using an organic metal compound as a starting gas, forming an organic layer having a high carbon concentration rich in organic property on the surface side of the base material, and continuously forming a metal oxide layer rich in inorganic property having a high metal concentration on the organic layer (see patent document 3). In the thus formed vapor deposited film, an organic layer is formed on the lower side of the metal oxide layer having a high gas-barrier property, i.e., on the surface side of the base material. Therefore, the vapor deposited film exhibits excellent gas-barrier property, high adhesiveness to the base material such as plastic material, and excellent flexibility.
Patent document 3: JP-A-2005-89859
However, the vapor deposited film disclosed in the patent document 3, too, still leaves much room for improvement. That is, the vapor deposited film having a layer structure in which an organic layer having a high carbon concentration is formed on the side of the surface of the base material and an inorganic metal oxide layer having a high gas-barrier property is formed on the above organic layer, has a defect of low heat resistance. Therefore, if the vapor deposited film is formed on the surface of the plastic container, the metal in the vapor deposited film elutes out into the content solution and the film thickness decreases particularly when the container is filled with the solution of a high temperature or when the container is preserved at a relatively high temperature (50 to 60° C.).